The present invention relates generally to dental prosthesis and, more particularly, to a retrievable dental prosthesis fabricated by using a special plastic cylinder during lost-wax casting procedures for the purpose of eliminating the need for a visible titanium abutment cylinder typically used for a conventional prosthesis in order to improve the appearance and functional features of the prosthesis.
In the past, the development of osseointegrated implants has allowed dental restorations or prostheses to be used with conventional titanium implants placed in a patient's bone structure underlying missing teeth for the purpose of replacing the lost teeth. Osseointegration (or bonding between the bone and implant) occurs so that the implant functions as a secure base on which to support a prosthesis. A conventional titanium (transmucosal) abutment cylinder is connected to the implant. The abutment is typically cemented to the implant or attached to it by a screw. As such, the abutment cylinder emerges from a patient's soft tissue (gum) and provides a structure upon which to mount the prosthesis. A prosthesis shaped like a tooth usually having a conventional cylinder incorporated into it is typically connected to the abutment cylinder by a screw.
Some problems have resulted in the past when a conventional titanium abutment cylinder has been used. For example, the titanium abutment cylinder extends from a patient's gum tissue (from the gingival crest) presenting an undesirable appearance due to the visible metallic cylinder. Also, inadequate interocclusal space between the abutment cylinder and opposing dentition may result in insufficient space for a conventionally designed prosthesis. Even when the shortest titanium abutment cylinder (3 mm) is used, the conventional cylinder incorporated within the prosthesis may be too large for the available working space. The heights of the conventional cylinder and the head of the cylinder screw may be decreased to accommodate the reduced working space, but this may compromise the integrity of the prothesis.
A conventional prosthesis typically uses a titanium abutment cylinder that is either cemented to an implant or secured to it by a screw. Rotation of the abutment cylinder with respect to the implant is prevented by cementing the two parts together or using male and female mating surfaces (e.g., hexagonal extension from implant mating with internal hexagonal surfaces in abutment cylinder). However, the conventional cylinder is not cemented to the abutment cylinder, nor do these two parts have mating male and female surfaces that prevent rotation of the parts. A screw holds the conventional cylinder to the titanium abutment cylinder.
Loosening and rotation of the conventional and titanium abutment cylinders with respect to each other will take place when the cylinders experience sufficient rotational forces and vibration. Rotation and loosening would be less likely if the prosthesis is anchored to another prosthesis, or a natural tooth (or adjacent teeth). However, prostheses using such anchoring means to prevent loosening and rotation thereof are more expensive and less attractive in appearance than a prosthesis not using such anchoring means.
Another disadvantage of some conventional prostheses relates to the difficulty in treating infections or other dental problems that may develop in those dental cases where the titanium abutment cylinder is cemented to the implant. In such cases, surgery may be required to remove the cemented parts in order to treat the problem areas.
Many of these problems would be eliminated or improved by providing a prosthesis directly connected at its base to an implant that may be easily removed from the implant and that uses mating male and female surfaces to prevent rotation. The prior art does not disclose or suggest such a prosthesis, which would eliminate the need for an unsightly titanium abutment cylinder, provide increased working space between the implant and a corresponding upper or lower tooth due to elimination of the abutment cylinder, prevent rotation of the prosthesis with respect to the implant, and allow removal of the prosthesis for maintenance, oral hygiene, or when infections occur.
In addition, proper dental hygiene may be difficult when a titanium abutment cylinder is used because the titanium abutment cylinder may not provide appropriate hygiene access or desirable contours near soft tissue areas adjacent the cylinder required for oral hygiene and a healthy gingival response. Also, plaque tends to accumulate more readily on a machined metal surface, such as a titanium abutment cylinder, than on, for example, a polished porcelain surface.